Pulmonary embolism, in which emboli from any of various regions of the vascular system pass into the lungs, accounts for thousands of deaths each year in the United States. Pulmonary embolisms typically occur when blood clots from the lower extremities are carried to the heart through the inferior vena cava (IVC), and from there to the pulmonary arteries within the lungs.
Many patients with documented pulmonary embolism (PE) can be treated with anti-coagulants to prevent further formation of thrombi, but there are situations in which mechanical interruption of the inferior vena cava is the preferred method to prevent pulmonary embolism. To prevent blood clots from passing upwardly through the inferior vena cava, filters have been placed in the vessel to trap potentially dangerous blood clots.
Conventional implantable blood filters employing a variety of geometries are known. Many are generally basket or cone shaped in order to provide adequate clot-trapping area while permitting sufficient blood flow. Also known are filters formed of various loops of wire, including some designed to partially deform the vessel wall in which they are implanted. Vena cava filters commonly include a core portion from which a plurality of wires radiate outwardly. The wires serve to filter clots from blood flowing through the vein. Various hook-like projections, barbs and the like have been suggested for use in holding the filter in place once the delivery catheter has been withdrawn.
Traditional indications for filters are patients with deep venous thrombosis, and with a contraindication for anticoagulation, or patients with large floating clots in the iliac veins or IVC, with an imminent risk of embolism. Additional contraindications are young patients or patients with a transient problem that may cause PE, not requiring a permanent filter. However, one important problem with many available intravascular filters in use is the non-retrievability of the devices, because while penetration of the retaining hooks of the filter into the lumen of the IVC is necessary for the proper anchoring of the device, in extreme cases and over time, over-penetration may impinge upon adjacent organs, leading to serious or even fatal complications. Further, with time the filter will be integrated into the aortic wall, making it unretrievable without causing significant damage to the vessel wall, particularly at the body of the basket. Accordingly, a vena cava filter capable of temporary deployment is desired to provide rapid protection against pulmonary embolism. However, as the condition producing blood clots is successfully treated, it may be desired to remove the filter from the vena cava.
There is therefore a need for a safe and effective intravascular filter that can be left in place permanently or deployed and subsequently removed by minimally invasive techniques and without causing substantial damage to the vessel wall, even after passage of such time that portions of the filter wires become integrated into the aortic wall.